We have the same situation. Flying with our 18 month old next month.
We are taking color wonders, a travel magnidoodle, stickers, animal crackers, cheese nips, a little sandwich, and a sippy cup of ice water. I'm also packing a blankie, although it's doubtful he'll sleep.
I thought about a sucker and I tested him out on his first one a couple weeks ago. It was a mess. He didn't swallow...he just let the slober/juice run out his mouth. What a sticky mess.
I also got him aquadoodle disney mats (where you color with the little pen that you put water in). He must be too young. He'll do this for a few seconds and then he is not interested, but then he's not really interested in books yet either. I'm hoping the color wonders do better, at least there's more pens to play with.
I got a non-stop flight so we will be there in 2 hours.
I thought about getting a little backpack, but I figure I'll be the one who ends up carrying it, so I'm just taking his diaper bag. It has a comfy shoulder strap.
Enjoy your trip!